Many organic materials that are useful as thin films in electronic devices cannot be patterned using photolithography because they are not compatible with photoresist chemicals and processes. Thus, these materials are typically deposited by vapor deposition and patterned using shadow masking techniques to form patterned thin film layers for electronic devices.
It can be difficult, however, to obtain a uniform thin film layer over a relatively large area (that is, an area comparable to the size of the vacuum chamber used for the deposition) by vapor deposition. Using shadow masks for patterning relatively large areas can also be problematic. Often, the organic source materials to be deposited are powders. As illustrated in FIG. 1, a source, typically a Knudsen cell, 14 is used to hold the organic source material. The source material is heated and vaporized into an essentially upward pointing beam 16. A shadow mask 10 must therefore be positioned beneath a deposition substrate 12, with both the deposition substrate 12 and the shadow mask 10 suspended above the source 14. When relatively large polymeric shadow masks are used, however, the shadow mask can sag 17 as a result of gravity, which can lead to imprecise patterning and/or alignment of device layers. A downward pointing beam cannot be utilized, however, because the powder would spill out of a downward facing source.